Semiconductor device and method for fabricating the same

ABSTRACT

A method for fabricating semiconductor device includes the steps of: forming a first magnetic tunneling junction (MTJ) on a substrate; forming a first liner on the MTJ; forming a second liner on the first liner; forming an inter-metal dielectric (IMD) layer on the MTJ, and forming a metal interconnection in the IMD layer, the second liner, and the first liner to electrically connect the MTJ. Preferably, the first liner and the second liner are made of different materials.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a semiconductor device and method forfabricating the same, and more particularly to a magnetoresistive randomaccess memory (MRAM) and method for fabricating the same.

2. Description of the Prior Art

Magnetoresistance (MR) effect has been known as a kind of effect causedby altering the resistance of a material through variation of outsidemagnetic field. The physical definition of such effect is defined as avariation in resistance obtained by dividing a difference in resistanceunder no magnetic interference by the original resistance. Currently, MReffect has been successfully utilized in production of hard disksthereby having important commercial values. Moreover, thecharacterization of utilizing GMR materials to generate differentresistance under different magnetized states could also be used tofabricate MRAM devices, which typically has the advantage of keepingstored data even when the device is not connected to an electricalsource.

The aforementioned MR effect has also been used in magnetic field sensorareas including but not limited to for example electronic compasscomponents used in global positioning system (GPS) of cellular phonesfor providing information regarding moving location to users. Currently,various magnetic field sensor technologies such as anisotropicmagnetoresistance (AMR) sensors, GMR sensors, magnetic tunnelingjunction (MTJ) sensors have been widely developed in the market.Nevertheless, most of these products still pose numerous shortcomingssuch as high chip area, high cost, high power consumption, limitedsensibility, and easily affected by temperature variation and how tocome up with an improved device to resolve these issues has become animportant task in this field.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, a method forfabricating semiconductor device includes the steps of: forming a firstmagnetic tunneling junction (MTJ) on a substrate; forming a first lineron the MTJ; forming a second liner on the first liner; forming aninter-metal dielectric (IMD) layer on the MTJ, and forming a metalinterconnection in the IMD layer, the second liner, and the first linerto electrically connect the MTJ. Preferably, the first liner and thesecond liner are made of different materials.

According to another aspect of the present invention, a semiconductordevice includes a first magnetic tunneling junction (MTJ) on a substrateand a first metal interconnection on the MTJ. Preferably, the firstmetal interconnection comprises protrusions adjacent to two sides of theMTJ and bottom surfaces of the protrusions comprise a planar surface.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-6 illustrate a method for fabricating a semiconductor deviceaccording to an embodiment of the present invention.

FIG. 7 illustrates a structural view of a semiconductor device accordingto an embodiment of the present invention.

FIG. 8 illustrates a structural view of a semiconductor device accordingto an embodiment of the present invention.

FIG. 9 illustrates a structural view of a semiconductor device accordingto an embodiment of the present invention.

FIG. 10 illustrates a structural view of a semiconductor deviceaccording to an embodiment of the present invention.

FIG. 11 illustrates a structural view of a semiconductor deviceaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

Referring to FIGS. 1-6, FIGS. 1-6 illustrate a method for fabricating asemiconductor device, or more specifically a MRAM device according to anembodiment of the present invention. As shown in FIG. 1, a substrate 12made of semiconductor material is first provided, in which thesemiconductor material could be selected from the group consisting ofsilicon (Si), germanium (Ge), Si—Ge compounds, silicon carbide (SiC),and gallium arsenide (GaAs), and a MTJ region 14 and a logic region 16are defined on the substrate 12.

Active devices such as metal-oxide semiconductor (MOS) transistors,passive devices, conductive layers, and interlayer dielectric (ILD)layer 18 could also be formed on top of the substrate 12. Morespecifically, planar MOS transistors or non-planar (such as FinFETs) MOStransistors could be formed on the substrate 12, in which the MOStransistors could include transistor elements such as gate structures(for example metal gates) and source/drain region, spacer, epitaxiallayer, and contact etch stop layer (CESL). The ILD layer 18 could beformed on the substrate 12 to cover the MOS transistors, and a pluralityof contact plugs could be formed in the ILD layer 18 to electricallyconnect to the gate structure and/or source/drain region of MOStransistors. Since the fabrication of planar or non-planar transistorsand ILD layer is well known to those skilled in the art, the details ofwhich are not explained herein for the sake of brevity.

Next, metal interconnect structures 20, 22 are sequentially formed onthe ILD layer 18 on the MTJ region 14 and the edge region 16 toelectrically connect the aforementioned contact plugs, in which themetal interconnect structure 20 includes an inter-metal dielectric (IMD)layer 24 and metal interconnections 26 embedded in the IMD layer 24, andthe metal interconnect structure 22 includes a stop layer 28, an IMDlayer 30, and metal interconnections 32 embedded in the stop layer 28and the IMD layer 30.

In this embodiment, each of the metal interconnections 26 from the metalinterconnect structure 20 preferably includes a trench conductor andeach of the metal interconnections 32 from the metal interconnectstructure 22 on the MTJ region 14 includes a via conductor. Preferably,each of the metal interconnections 26, 32 from the metal interconnectstructures 20, 22 could be embedded within the IMD layers 24, 30 and/orstop layer 28 according to a single damascene process or dual damasceneprocess. For instance, each of the metal interconnections 26, 32 couldfurther includes a barrier layer 34 and a metal layer 36, in which thebarrier layer 34 could be selected from the group consisting of titanium(Ti), titanium nitride (TiN), tantalum (Ta), and tantalum nitride (TaN)and the metal layer 36 could be selected from the group consisting oftungsten (W), copper (Cu), aluminum (Al), titanium aluminide (TiAl), andcobalt tungsten phosphide (CoWP). Since single damascene process anddual damascene process are well known to those skilled in the art, thedetails of which are not explained herein for the sake of brevity. Inthis embodiment, the metal layers 36 are preferably made of copper, theIMD layers 24, 30 are preferably made of silicon oxide, and the stoplayers 28 is preferably made of nitrogen doped carbide (NDC), siliconnitride, silicon carbon nitride (SiCN), or combination thereof.

Next, a MTJ stack 38 or stack structure is formed on the metalinterconnect structure 22, a cap layer 40 is formed on the MTJ stack 38,and another cap layer 42 formed on the cap layer 40. In this embodiment,the formation of the MTJ stack 38 could be accomplished by sequentiallydepositing a first electrode layer 44, a fixed layer 46, a free layer48, a capping layer 50, and a second electrode layer 52 on the IMD layer30. In this embodiment, the first electrode layer 44 and the secondelectrode layer 52 are preferably made of conductive material includingbut not limited to for example Ta, Pt, Cu, Au, Al, or combinationthereof. The fixed layer 46 could be made of antiferromagnetic (AFM)material including but not limited to for example ferromanganese (FeMn),platinum manganese (PtMn), iridium manganese (IrMn), nickel oxide (NiO),or combination thereof, in which the fixed layer 46 is formed to fix orlimit the direction of magnetic moment of adjacent layers. The freelayer 48 could be made of ferromagnetic material including but notlimited to for example iron, cobalt, nickel, or alloys thereof such ascobalt-iron-boron (CoFeB), in which the magnetized direction of the freelayer 48 could be altered freely depending on the influence of outsidemagnetic field. The capping layer 50 could be made of insulatingmaterial including but not limited to for example oxides such asaluminum oxide (AlO_(x)) or magnesium oxide (MgO). Preferably, the caplayer 40 and cap layer 42 are made of different materials. For instance,the cap layer 40 is preferably made of silicon nitride and the cap layer42 is made of silicon oxide, but not limited thereto.

Next, a patterned mask 54 is formed on the cap layer 42. In thisembodiment, the patterned mask 54 could include an organic dielectriclayer (ODL) 56, a silicon-containing hard mask bottom anti-reflectivecoating (SHB) 58, and a patterned resist 60.

Next, as shown in FIG. 2, one or more etching process is conducted byusing the patterned mask 54 as mask to remove part of the cap layers 40,42, part of the MTJ stack 38, and part of the IMD layer 30 to form a MTJ62 on the MTJ region 14, in which the first electrode layer 44 at thisstage preferably becomes a bottom electrode 76 for the MTJ 62 while thesecond electrode layer 52 becomes a top electrode 78 for the MTJ 62 andthe cap layers 40, 42 could be removed during the etching process. Itshould be noted that this embodiment preferably conducts a reactive ionetching (RIE) process by using the patterned mask 54 as mask to removepart of the cap layers 40, 42 and part of the MTJ stack 38, strips thepatterned mask 54, and then conducts an ion beam etching (IBE) processby using the patterned cap layer 42 as mask to remove part of the MTJstack 38 and part of the IMD layer 30 to form MTJ 62. Due to thecharacteristics of the IBE process, the top surface of the remaining IMDlayer 30 is slightly lower than the top surface of the metalinterconnections 32 after the IBE process and the top surface of the IMDlayer 30 also reveals a curve or an arc.

It should also be noted that when the IBE process is conducted to removepart of the IMD layer 30, part of the metal interconnection 32 isremoved at the same time so that a first slanted sidewall 64 and asecond slanted sidewall 66 are formed on the metal interconnection 32adjacent to the MTJ 62, in which each of the first slanted sidewall 64and the second slanted sidewall 66 could further include a curve (orcurved surface) or a planar surface. Moreover, if the second electrodelayer 52 were made of tantalum (Ta), more second electrode layer 52closer to the tip of the MTJ 62 is preferably removed during thepatterning of the MTJ stack 38 through the IBE process so that inclinedsidewalls and top surfaces are formed on the patterned MTJ 62.Specifically, the tip or top portion the top electrode 78 of the MTJ 62formed at the stage preferably includes a reverse V-shape or a curve(not shown) while two sidewalls of the MTJ 62 are slanted sidewalls.

Next, as shown in FIG. 3, a liner 68 is formed on the MTJ 62 to coverthe surface of the IMD layer 30. In this embodiment, the liner 68 ispreferably made of silicon nitride (SiN), but could also be made ofother dielectric material including but not limited to for examplesilicon oxide, silicon oxynitride, or silicon carbon nitride.

Next, as shown in FIG. 4, an etching process is conducted to remove partof the liner 68 to form a spacer including a first spacer 70 and asecond spacer 82 adjacent to the MTJ 62, in which the first spacer 70 isdisposed on a sidewall of the MTJ 62 to cover and contact the firstslanted sidewall 64 of the metal interconnection 32 and the secondspacer 82 and the second spacer 82 is disposed on another sidewall ofthe MTJ 62 to cover an contact the second slanted sidewall 66.

Next, an atomic layer deposition (ALD) process is conducted to form asecond liner 100 to cover the surfaces of the IMD layer 30, the MTJ 62,the first spacer 70, and the second spacer 82. In this embodiment, thefirst liner 68 and the second liner 100 are preferably made of differentmaterials, in which the first liner 68 preferably includes siliconnitride (SiN) while the second liner 100 preferably includes siliconoxide or tetraethyl orthosilicate (TEOS). Nevertheless, according toother embodiments of the present invention, the two layers 68, 100 couldalso be selected from the group consisting of SiN, SiO₂, SiON, and SiCNwhile the two layers 68, 100 are made of different materials. Moreover,the thickness of the first spacer 70 and/or second spacer 82 could besubstantially the same as the thickness of the second liner 100.

Next, as shown in FIG. 5, another IMD layer 72 is formed on the MTJregion 14 and logic region 16, and a pattern transfer process isconducted by using a patterned mask (not shown) to remove part of theIMD layer 72 on the logic region 16 to form a contact hole (not shown)exposing the metal interconnection 26 underneath and metals aredeposited into the contact hole afterwards. For instance, a barrierlayer 34 selected from the group consisting of titanium (Ti), titaniumnitride (TiN), tantalum (Ta), and tantalum nitride (TaN) and metal layer36 selected from the group consisting of tungsten (W), copper (Cu),aluminum (Al), titanium aluminide (TiAl), and cobalt tungsten phosphide(CoWP) could be deposited into the contact holes, and a planarizingprocess such as chemical mechanical polishing (CMP) process could beconducted to remove part of the metals including the aforementionedbarrier layer and metal layer to form a contact plug 74 in the contacthole electrically connecting the metal interconnection 26.

Next, as shown in FIG. 6, a stop layer 80 and another IMD layer 86 areformed on the MTJ 62 to cover the surface of the IMD layer 72, and oneor more photo-etching process is conducted to remove part of the IMDlayer 86, part of the stop layer 80, part of the IMD layer 72, part ofthe second liner 100, and even part of the spacer adjacent to the MTJ 62on the MTJ region 14 and part of the IMD layer 86 and part of the stoplayer 80 on the logic region 16 to form contact holes (not shown). Next,conductive materials are deposited into each of the contact holes and aplanarizing process such as CMP is conducted to form metalinterconnections 88, 90 directly connecting the MTJ 62 and contact plug74 on the MTJ region 14 and logic region 16, in which the metalinterconnection 88 including protrusions 98 on the MTJ region 14preferably directly contacts the MTJ 62 and/or left and right sidewallsof the top electrode 78 underneath while the metal interconnection 90 onthe logic region 16 directly contacts the contact plug 74 on the lowerlevel. Next, another stop layer 96 is formed on the IMD layer 86 tocover the metal interconnections 88, 90. In this embodiment, the widthof the metal interconnection 88, especially the via conductor of themetal interconnection 88 directly contacting the MTJ 62 is preferablygreater than the width of the MTJ 62, the bottom of each of theprotrusions 98 or protruding portions include a planar surface, and thebottom surfaces of the protrusions 98 are preferably higher than the topsurface of the capping layer 50. Moreover, the bottom surface of each ofthe protrusions 98 contact the first spacer 70 and the second spacer 82respectively, the sidewalls of each of the protrusions 98 are alignedwith sidewalls of the first spacer 70 and the second spacer 82, and thethickness or width of each of the first spacer 70 and the second spacer82 could be less than or equal to the thickness or width of the secondliner 100.

In this embodiment, the stop layer 80 and the stop layer 28 could bemade of same material or different material. For example, both layers80, 28 could include nitrogen doped carbide (NDC), silicon nitride,silicon carbon nitride (SiCN), or combination thereof. Similar to themetal interconnections formed previously, each of the metalinterconnections 88, 90 could be formed in the IMD layer 86 through asingle damascene or dual damascene process. For instance, each of themetal interconnections 88, 90 could further include a barrier layer 92and a metal layer 94, in which the barrier layer 92 could be selectedfrom the group consisting of titanium (Ti), titanium nitride (TiN),tantalum (Ta), and tantalum nitride (TaN) and the metal layer 94 couldbe selected from the group consisting of tungsten (W), copper (Cu),aluminum (Al), titanium aluminide (TiAl), and cobalt tungsten phosphide(CoWP). Since single damascene process and dual damascene process arewell known to those skilled in the art, the details of which are notexplained herein for the sake of brevity. This completes the fabricationof a semiconductor device according to an embodiment of the presentinvention.

Referring to FIG. 7, FIG. 7 illustrates a structural view of asemiconductor device according to an embodiment of the presentinvention. As shown in FIG. 7, in contrast to the bottom surfaces of theprotrusions 68 directly contacting the top surfaces of the first spacer70 and the second spacer 82 while sidewalls of each of the protrusions98 are aligned with sidewalls of the first spacer 70 and second spacer82 respectively as shown in FIG. 6, it would also be desirable to widthof the protrusions 98 such that the bottom surfaces of the protrusions98 directly contact the top surface of the first spacer 70, the topsurface of the second spacer 82, and the top surface of the second liner100 while sidewalls of the protrusions 98 are aligned with sidewalls ofthe second liner 100, which is also within the scope of the presentinvention.

Referring to FIG. 8, FIG. 8 illustrates a structural view of asemiconductor device according to an embodiment of the presentinvention. As shown in FIG. 8, in contrast to the top electrode 78 beingmade of tantalum (Ta) as shown in FIG. 6, the top electrode 78 of thisembodiment is preferably made of titanium nitride (TiN) so that when thesecond electrode layer 52 is patterned by etching process to form theMTJ 62 in FIG. 2 the top electrode 78 of the MTJ 62 preferably includesa planar top surface and planar and vertical sidewalls. Next,fabrications illustrated in FIGS. 3-6 are conducted to form a firstliner 62 on sidewalls of the MTJ 62, remove part of the first liner 68to form a first spacer 70 and second spacer 82 adjacent to the MTJ 62,form a second liner 100 to cover the IMD layer 30, the MTJ 62, the firstspacer 70, and the second spacer 82, form an IMD layer 72, a stop layer80, and another IMD layer 86 on the MTJ 62, and form metalinterconnections 88, 90 connecting the MTJ 62 and metal interconnection72.

Referring to FIG. 9, FIG. 9 illustrates a structural view of asemiconductor device according to an embodiment of the presentinvention. As shown in FIG. 9, it would also be desirable to first formthe first liner 68 as shown in FIG. 3, skip the etching processconducted in FIG. 4, and then directly form a second liner 100 on thesurface of the first liner 68. Next, processes conducted in FIGS. 5-6could be carried out to form an IMD layer 72, a stop layer 80, andanother IMD layer 86 on the second liner 100, and finally form metalinterconnections 88, 90 to connect the MTJ 62 and the metalinterconnection 74 respectively.

It should be noted since the first liner 68 has not been etched to formspacers in this embodiment, the first liner 68 itself after beingdeposited on the surface of the IMD layer 30 and MTJ 62 preferablyinclude uneven thickness. For instance, the portion of the first liner68 disposed on or directly contacting sidewalls of the MTJ 62 and theportion of the first liner 68 disposed on or directly contacting the topsurface of the IMD layer 30 preferably include different thicknesses, inwhich the thickness of the first liner 68 directly contacting sidewallsof the MTJ 62 is preferably less than the thickness of the first liner68 directly contacting the top surface of the IMD layer 30. In thisembodiment, the thickness of the first liner 68 disposed on thesidewalls of the MTJ 62 is preferably between 5-30 nm while thethickness of the first liner 68 disposed on the top surface of the IMDlayer 30 is between 6-40 nm. In contrast to the first liner 68 havinguneven thickness, the second liner 100 disposed on the surface of thefirst liner 68 preferably includes an even thickness while the thicknessof the second liner 100 is preferably equal to the thickness of thefirst liner 68 disposed on sidewalls of the MTJ 62 or between 5-30 nm.

Referring to FIG. 10, FIG. 10 illustrates a structural view of asemiconductor device according to an embodiment of the presentinvention. As shown in FIG. 10, it would be desirable to form a topelectrode 78 made of TiN as shown in FIG. 8, and then follow theembodiment as disclosed in FIG. 9 to form a first liner 68 according toFIG. 3, skip the etching process conducted in FIG. 4, and then directlyform a second liner 100 on the surface of the first liner 68. Next,processes conducted in FIGS. 5-6 could be carried out to form an IMDlayer 72, a stop layer 80, and another IMD layer 86 on the second liner100, and finally form metal interconnections 88, 90 to connect the MTJ62 and the metal interconnection 74 respectively.

Similar to the embodiment disclosed in FIG. 9, since the first liner 68has not been etched to form spacers in this embodiment, the first liner68 itself after being deposited on the surface of the IMD layer 30 andMTJ 62 preferably include uneven thickness. For instance, the portion ofthe first liner 68 disposed on or directly contacting sidewalls of theMTJ 62 and the portion of the first liner 68 disposed on or directlycontacting the top surface of the IMD layer 30 preferably includedifferent thicknesses, in which the thickness of the first liner 68directly contacting sidewalls of the MTJ 62 is preferably less than thethickness of the first liner 68 directly contacting the top surface ofthe IMD layer 30. In this embodiment, the thickness of the first liner68 disposed on the sidewalls of the MTJ 62 is preferably between 5-30 nmwhile the thickness of the first liner 68 disposed on the top surface ofthe IMD layer 30 is between 6-40 nm. In contrast to the first liner 68having uneven thickness, the second liner 100 disposed on the surface ofthe first liner 68 preferably includes an even thickness while thethickness of the second liner 100 is preferably equal to the thicknessof the first liner 68 disposed on sidewalls of the MTJ 62 or between5-30 nm.

Referring to FIG. 11, FIG. 11 illustrates a structural view of asemiconductor device according to an embodiment of the presentinvention. As shown in FIG. 11, it would be desirable to combine theembodiments from FIG. 7 and FIG. 9 by first forming a first liner 68according to FIG. 3, skip the etching process conducted in FIG. 4, andthen directly form a second liner 100 on the surface of the first liner68. Next, processes conducted in FIGS. 5-6 could be carried out to forman IMD layer 72, a stop layer 80, and another IMD layer 86 on the secondliner 100, and finally form metal interconnections 88, 90 to connect theMTJ 62 and the metal interconnection 74 respectively.

Moreover, similar to FIG. 7, in contrast to the bottom surface of theprotrusions 98 contacting the top surfaces of the first spacer 70 andthe second spacer 82 while sidewalls of the protrusions 98 are alignedwith sidewalls of the first spacer 70 and second spacer 82, it would bedesirable to adjust the width of the metal interconnection 88 so thatthe bottom surfaces of the protrusions 98 contact the top surfaces ofthe first spacer 70, second spacer 82, and second liner 100 whilesidewalls of the protrusions 98 are aligned with sidewalls of the secondliner 100, which is also within the scope of the present invention.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A semiconductor device, comprising: a firstmagnetic tunneling junction (MTJ) on a substrate; a first metalinterconnection on the MTJ, wherein the first metal interconnectioncomprises protrusions adjacent to two sides of the MTJ and bottomsurfaces of the protrusions comprise a planar surface; a first spacer onone side of the MTJ; a second spacer on another side of the MTJ, whereinthe first spacer and the second spacer contact the protrusions directlyand outer sidewalls of the protrusions are aligned with outer sidewallsof the first spacer and the second spacer; and a liner adjacent to thefirst MTJ, wherein the liner contacts a sidewall of the first metalinterconnection directly.
 2. The semiconductor device of claim 1,further comprising: a first inter-metal dielectric (IMD) layer aroundthe liner.
 3. The semiconductor device of claim 1, further comprising: asecond metal interconnection under the MTJ; and a second IMD layeraround the second metal interconnection.
 4. The semiconductor device ofclaim 3, wherein the MTJ comprises: a bottom electrode on the secondmetal interconnection; a barrier layer on the bottom electrode; and atop electrode on the barrier layer.
 5. The semiconductor device of claim4, wherein a bottom surface of the protrusions is higher than a topsurface of the barrier layer.
 6. The semiconductor device of claim 1,wherein a width of the first metal interconnection is greater than awidth of the MTJ.